restoring question from beginner

I have two large pine bookcases that I finished about 10 years ago. They are stained dark. I forget if there is water or oil based polyurethane on them, but there are two coats of it.
My problem is that the grain was raised and so it is somewhat rough, which makes dusting difficult. I was thinking if I sand and put a couple more coats of finish on it, it may smooth it out. Am I incorrect on this point? Does it matter if I put water based or oil based polyurethane on it, not knowing what's underneath?
thanks for any advise, Bonnie
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Bonnie Jean did say:

You're correct. Sand the existing finish and put on a new coat of poly. if you need to use multiple coats, lightly sand between each. It shouldn't matter if you use water or oil based.
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Bonnie Jean did say:

Thanks Woodmangler.
Water or oil based polyurethane......is one considered better than another?
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Bonnie Jean did say:

I seldom use poly, so others may have differing opinions: They're both reactive finishes and do not combine with previous coats, so for good adhesion you'll want to lightly sand either one before applying another coat. Oil based dries somewhat slower so will take more time, but may flow a little better than water based, so may level out and create a smoother finish. Water based may raise the grain a bit when applied to bare wood, but you're past that point. Either one will give you a good hard protective finish. I think I'd suggest an oil based, probably a little easier to get a nice smooth finish. Just takes a bit longer to dry.
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I agree. I've used both (not on the same project) and I prefer the final finish the oil-based ones give. The extra clean up and time-to-dry is worth it. I *generally* just hit a coat before I leave for work in the morning and/or one before turning in for the evening, so I don't really notice the time-to-dry issue. If you're careful with application you can use cheap, throw-away brushes and avoid more clean up issues.
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Oil imparts an ambering color while water doesn't and water dries faster without much odor.
wrote:

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wrote:

If you're using steel wool don't use water based poly.
Thunder
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I asked: Water or oil based polyurethane......is one considered better than another?
Thanks to all for your responses. You've been a big help.
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Won't matter a bit. Knock the finish down with some fine sandpaper to smooth it out and put on whatever you have around now - oil base or water base. Once this stuff dries the carrier is gone and it does not matter which one you put over it later on.
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